1. Field of Invention
The present invention relates generally to the field of providing video services. More specifically, the present invention relates to transmittal and storage of electronic program guide data.
2. Background of the Invention
Conventional set top boxes distribute video services to subscribers over a number of media, including cable, satellite, broadcast and terrestrial systems. These video services include (1) traditional broadcast and cable television programs, (2) video services, such as pay-per-view, near video-on-demand, promotional channels, electronic programming guides (EPGs), and localized or specially formatted information, (3) cable delivered PC-based content and services, and (4) interactive services. The term set top box (STB) refers to any interface device used to interface the video services provided by a service provider to a subscriber's graphic display device, such as a television, over one of the aforementioned media.
The video services are transmitted in constructs called transports. Each transport carries one or more video services from a service provider to a subscriber. FIG. 1 illustrates an exemplary transport architecture 100. Transport architecture 100 includes a home transport 104 and n non-home transports 106i–106N. Each transport is transmitted on a unique frequency (or other transmission paradigm, for example, a transponder in the case of satellite).
Home transport 104 contains a full event information table (EIT) data set. The full EIT data carries all information corresponding to a 7-day period of events. Each event contains information related to the services carried in the transports, for example, television programming information (e.g., date start times, duration and description). The full EIT contains 56 segments, where each segment corresponds to 3 hours of event data. The full EIT is transmitted at a high spool rate. Spool rate refers to the bandwidth allocated for the data, preferably in bytes per second.
Home transport 104 includes other system information (SI) data. Such other SI data includes network information tables (NITs), service information tables (SITs), program association table (PAT), program map table (PMT) and others. This information is defined by the DVD standard for SI information. See, “ETS 300 468, Digital Broadcasting Systems for Television, Sound and Data Services; Specification for Service Information (SI) in Digital Video Broadcasting Systems (DVB) Systems,” which is hereby incorporated by reference herein in its entirety.
Home transport 104 also carries several services, i.e., the audio and visual data for a particular television channel, such as HBO. There are N services, service 1104 through service N104 shown in the exemplary home transport. Conventionally, home transport 104 carries data associated with 3 of the provided services, as well as the overhead data described above.
There are N non-home transports 1061 through 106N. Conventionally, each non-home transport can carry data associated with 6 services. Five of the services are audio and visual program content. The sixth service is partial EIT data. The partial EIT data, is 2 segments of event data (corresponding to 6 hours of events) for all services. The partial EIT is transmitted at a high spool rate.
The number of transports is dependent upon the number of services that can be carried in a particular transport. Although conventional transports have data carrying capacities for carrying approximately 6 services, compression schemes have been developed which increase the number of services carried by each transport. Conventionally, the data in the segments is organized by service. That is, all of the data pertaining to service 1104 is sent, followed by all of the data for service 2104 and so on until all of the data for the service N104 is sent.
Conventional set top boxes store only a small portion of the full EIT data stream. This is because they store all event information for every event in that stream. Unfortunately, conventional set top boxes only have on the order of 300 KB of memory for storing EIT data. This is far short of the approximately 3.5 megabytes of memory required on average to store all of the data sent on the full EIT data stream. In fact, only 2 segments or 6 hours of event data is stored in conventional STBs without compression. Even using complex compression schemes allows only up to 2 days of data to be stored. Thus, if a subscriber desires to view event data in the future, for example, 5 days from the present, the STB must somehow load this data so the subscriber can access it.
To view EIT information, a user scrolls through, for example, an electronic programming guide (EPG). The EPG is an application executing, for example, on a microprocessor in the STB, which displays to the user available programming for the time period of interest. However, if the subscriber wants to access any information beyond the information stored in the STB, and he or she is on any transport other than the home transport, the system will have to interrupt his or her viewing of the program to go get that information. This is because the set top box must tune to the home transport, wait for the program information pertaining to the subscriber's request to be downloaded, process that information, present it to the subscriber and then tune back to the non-home transport on which the subscriber's program is being carried. Such interruption is likely in most cases since the home transport carries very few of the services the subscriber may wish to access.
The ability to view EPG data without interrupting another service is particularly important in applications such as picture-in-picture (PIP). In the case of PIP, the subscriber views EPG data as part of the main screen or the picture-in-picture screen, while simultaneously viewing the original program. However, the convenience of PIP is greatly diminished if the set top box does not have all of the information for the 7-day period available to it, because the PIP screen must constantly be interrupted to get the EIT data for display on the EPG.